INTRODUCTION

　　Most portable computers have built-in sockets to accept small PC cards for use as extended memories， fax modems， network interfaces， wireless communicators and a wide assortment of other functions. The Personal Computer Memory Card International Association （PCMCIA） has released specifications that outline the general power requirements for these cards.

　　The specification calls for an unusual amount of voltage switching. Both supplies are switchable to different voltages to accommodate a wide range of card types. The VCC supply must provide either 3.3V or 5V. The VPP supply must source 12V， 3.3V， 5V， 0V and realize a high impedance state. These diverse， specific requirements call for specialized solutions.

　　PC card designers may want to design their cards to require the VCC supply only. Flash memory card designers who need to ensure a clean VPP supply may generate their own 12V on the card. Type I PC cards， at an outside thickness of 3.3mm， require ultra-thin highly efficient circuitry. The DC/DC converter IC， inductor， capacitors and diodes are critical components that require unique design to meet the stringent height requirements.